[Pw_forum] Workfunction from slab calculations?

[Georg Heimel]

----- Original Message ----- 
From: "Paolo Giannozzi" <giannozz at nest.sns.it>
To: <pw_forum at pwscf.org>
Sent: Monday, August 02, 2004 1:01 PM
Subject: Re: [Pw_forum] Workfunction from slab calculations?


> On Thursday 29 July 2004 19:03, Georg Heimel wrote:
>
> > i guess that some constants have been dropped in PWscf
> > (like v_c(G=0) or the "alpha"-term from the pseudopotentials).
>
> not that I know. The potential at G=0 is given by the "alpha"-term
> (the limit of (V_H+V_loc)(G) for G->0) plus V_xc(G=0).

Thanks for the reply! May I ask, where in PWscf one can access this term
(these terms)?

The problem is that, obviously, something is not added back on before the
eigenvalues and the fermi energy is printed out. Howelse could they be
positive and scale with the inverse of the unit cell volume V (vacuum
thickness in a slab calculation)?

Having acess to these 1/V dependent term and adding them back on should give
you a Fermi energy that is more or less independent of the vacuum layer
thickness (provided it is large enough to start with).

Furthermore, the value of the full kohn-sham potential in the middle vacuum
region also scales with 1/V. Adding back on any potentially dropped term
would give a far quicker "convergence" = removal of the extrinsic 1/V
dependence.

Because of this strange 1/V behavior of the respective quantities, the
workfunction with PWscf is always calculated as difference between
fermi-energy and hartree-only potential in the vacuum region. This, however,
is not necessary with other codes, that provide you with "absolute" values
for the fermi energy, eigenvalues and potential in the first place.

I would greatly appreciate further comments on that.

Many thanks in advance!

Georg Heimel


========================================
DI Dr. Georg Heimel
School of Chemistry & Biochemistry
Georgia Institute of Technology
Atlanta, GA 30332-0400
USA
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EMail: georg.heimel at chemistry.gatech.edu
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